Tissue products, such as facial tissues, paper towels, bath tissues, sanitary napkins, and other similar products, are designed to include several important properties. For example, the products should have good bulk, a soft feel, and should have good strength. Unfortunately, however, when steps are taken to increase one property of the product, other characteristics of the product are often adversely affected.
For example, during a papermaking process, it is common to use various resins to increase the wet strength of the web. Cationic resins, for example, are often used because they are believed to more readily bond to the anionically charged cellulosic fibers. In addition, resins that are anionic in nature have also been utilized. U.S. Pat. No. 3,844,880 to Meisel, Jr., et al., for instance, describes anionic styrene-butadiene latexes that are adhered to the anionic cellulosic fibers with a deposition aid. Although strength resins can increase the strength of the web, they also tend to stiffen the web, which is often undesired by consumers. Thus, various methods are often used to counteract this stiffness and to soften the product. For example, chemical debonders can be utilized to reduce fiber bonding and thereby increase softness.
Nevertheless, reducing fiber bonding with a chemical debonder can sometimes adversely affect the strength of the tissue product. For example, hydrogen bonds between adjacent fibers can be broken by such chemical debonders, as well as by mechanical forces of a papermaking process. Consequently, such debonding results in loosely bound fibers that extend from the surface of the tissue product. During processing and/or use, these loosely bound fibers create zones of fibers that are poorly bound to each other and adjacent zones of fibers. As a result, during use, certain shear forces can liberate the weakly bound zones from the remaining fibers, thereby resulting in slough, i.e., bundles or pills on surfaces, such as skin or fabric. Thus, the use of such debonders can sometimes result in a much weaker paper product during use that exhibits substantial amounts of slough.
As such, a need currently exists for a tissue product that is strong, soft, and that also has low slough.
In accordance with one embodiment of the present invention, a method is provided for forming a tissue product. The method includes providing a liquid furnish of cellulosic fibers and forming a multi-layered wet web from the liquid furnish of cellulosic fibers. The wet web is dried to a solids consistency of about 90% or greater, such as with one or more through-dryers. At least one latex (e.g., nonionic or anionic) is applied to the dried web (e.g., foamed, printed, sprayed, etc.) in an amount less than about 3% of the dry weight of said web, in some embodiments, from about 0.1% to about 1.5% of the dry weight of the web, and in some embodiments, from about 0.5% to about 1% of the dry weight of the web. The latex remains substantially uncured after being applied to the dried web. For instance, in some embodiments, the dried web remains at a temperature below about 130xc2x0 C. after being applied with the latex. The latex has a glass transition temperature that is less than about 30xc2x0 C., and in some embodiments, that is also greater than about xe2x88x9225xc2x0 C. For example, in some embodiments, the glass transition temperature is from about xe2x88x9215xc2x0 C. to about 15xc2x0 C., and in some embodiments, from about xe2x88x9210xc2x0 C. to about 0xc2x0 C. The latex can be selected from the group consisting of styrene-butadiene copolymers, polyvinyl acetate homopolymers, vinyl-acetate ethylene copolymers, vinyl-acetate acrylic copolymers, ethylene-vinyl chloride copolymers, ethylene-vinyl chloride-vinyl acetate terpolymers, acrylic polyvinyl chloride polymers, acrylic polymers, and nitrile polymers.
In some embodiments, the surface of the multi-layered dried web has elevated regions and non-elevated regions. The latex may be applied to the dried web such that a greater amount of the latex resides on the elevated regions than on the non-elevated regions. Generally, the latex may be applied to the web in a variety of ways. For instance, the latex may be applied to the web as a foam composition. The foam composition may have a blow ratio greater than about 3:1 before being applied to the dried web. Alternatively, the latex may be applied by printing, spraying, as well as other techniques.
In accordance with another embodiment of the present invention, a tissue product is disclosed that comprises a multi-layered paper web having at least one outer layer that defines an outer surface of the tissue product. The outer layer comprises a substantially uncured latex having a glass transition temperature less than about 30xc2x0 C. and greater than about xe2x88x9225xc2x0 C. If desired, one or more of the remaining layers of the multi-layered paper web may remain substantially free of the latex.
Other features and aspects of the present invention are discussed in greater detail below.